Abstract: Test research was made on the preparation of polysilicate ferrite (PSF) flocculant by the process of acid leaching, catalytic oxidation, hydrolysis and polymerization with low grade hematite, spent sulfuric acid and sodium silicate. The results show that the optimal process conditions include: sulfuric acid concentration of 5～6 mol/L ; liquid-solid ratio of 4∶1, acid leaching temperature of 90 ℃, acid leaching time of 2～3 h, oxygen flowrate of 40 cm³/（min·L）,  Fe/Si mol ratio of 2, pH value of 3 for activating silicate, silicate activating time of 25 min and aging time of 2 h. The resultant PSF was used in treating the waste water from printing and dyeing and was compared with polymerized ferric sulfate (PFS) and polyaluminium chloride (PAC). The results show that at a dosage of 90 mg/L, PSF can remove the turbidity, chroma, SS and COD_Cr from the waste water by 91.5%, 87.8%, 92.2% and 78.5% respectively, 10, 24, 14 and 18 percentage points higher respectively than those by PFS and PAC at the same dosage.

Key words: Hematite, Polysilicate ferrite flocculant, Treatment of waste water, Flocculation performance